1. Field of the Invention
The invention relates to an exhaust heat recovery system which is used in an automobile such as a hybrid vehicle, and which recovers heat energy contained in gas so as to convert the heat energy contained in the gas to electric energy.
2. Description of the Related Art
Heat energy is contained in exhaust gas, and the like, that is discharged from an engine of an automobile. Accordingly, if the exhaust gas is simply discharged, the energy is wasted. To address this concern, technologies have been developed that utilize an exhaust heat recovery system to recover the heat energy contained in exhaust gas, and convert it to electric energy using a thermoelectric conversion element. The converted electric energy can then be used, for example, to recharge a battery.
An example of such an exhaust heat recovery system is disclosed in Japanese Patent Laid-Open Publication No. 2003-65045. In the exhaust heat recovery system, a heat pipe is connected to a component of an exhaust system for an engine, and a thermoelectric element (thermoelectric conversion element) is connected to the heat pipe. Also, a catalyst for purifying exhaust gas is provided in the exhaust system for the engine. Thus, since heat in the exhaust system is transferred to the thermoelectric element using the heat pipe, electric power generation efficiency of the thermoelectric element is improved, and efficiency of recovering engine exhaust heat is improved.
Meanwhile, the catalyst provided in the exhaust system for the engine offers intrinsic purification performance when a temperature of the catalyst reaches an activation temperature at which the catalyst is activated. Accordingly, when the catalyst is cold, for example, when then engine is started, the purification performance of the catalyst can be obtained early by completing warming-up of the catalyst early.
However, in the exhaust heat recovery system disclosed in the Japanese Patent Laid-Open Publication No. 2003-65045, since the heat contained in exhaust gas is transferred to the thermoelectric conversion element using the heat pipe, an amount of heat contained in the exhaust gas transported to the catalyst is decreased. Therefore, there is a problem that it takes a long time to complete warming-up of the catalyst.
In order to solve the problem, for example, it is conceivable to perform ON-OFF control of the thermoelectric element such that the thermoelectric element is turned off when warming-up of the catalyst is performed. However, in order to perform such ON-OFF control of the thermoelectric element, it is necessary to provide a control device, On-Off switching means, a temperature sensor for detecting a temperature of the catalyst, and the like. Therefore, there is a problem that configuration of the exhaust heat recovery system becomes complicated, and size thereof is increased.